Project Summary Initiation of antiretroviral therapy (ART) at a young age in perinatally-infected children has been shown to reduce the size of the ?viral reservoir,? which is considered the primary obstacle to HIV cure or remission. Critical to expanding our understanding of how early ART initiation influences HIV pathogenesis is expanding the range of biomarkers that can help track these processes. Here we propose a molecular epidemiology study to investigate the extent to which oral microbial signatures can be used as biomarkers to predict clinically-relevant virologic and immunologic changes among early-treated, HIV-infected infants and children. Finding a biomarker in oral samples would be clinically-useful as non-invasive sampling is always preferred. We propose to characterize oral microbial communities in two cohorts of HIV-infected infants and children enrolled at Rahima Moosa Mother and Child Hospital in Johannesburg, South Africa. Cohort 1 is a cohort of 260 perinatally-infected children now between 10-12 years of age who have been well-controlled on ART since initiating it when under 2 years of age. In parallel with Cohort 1 is a cohort of 220 age-matched HIV-uninfected children from the same community. Cohort 2 is a cohort of intrauterine-infected children initiated on ART within the neonatal period. Recruitment into this cohort started 3 years ago and is on-going. In parallel with Cohort 2 is a cohort of HIV-exposed, uninfected infants recruited at birth. We propose to test oral samples from selected time-points from these cohorts. We will characterize bacterial communities in these oral samples using targeted 16S rRNA sequencing. Specific Aim 1 will test the hypothesis that earlier initiation of ART (under 3 months of age) will leave distinct microbial signatures in the oral cavity detectable in pre-adolescent children well-controlled on ART. Specific Aim 2 will test the hypothesis that oral microbial signatures will be associated with the size of the viral reservoir in older pre-adolescent perinatally-infected children well-controlled on ART as well as in intrauterine-infected infants and young children initiating ART during the neonatal period. Specific Aim 3 will describe age-related dynamics in oral microbial communities between very early (<48 hours of life) treated intrauterine-infected infants and HIV-exposed uninfected infants. We have designed a large and rigorous epidemiologic study in the southern African population most affected by the HIV epidemic. We have unique cohorts that can be studied to determine whether oral microbial signatures are associated with known parameters relevant to HIV remission.